1. Field of technology
The present invention relates to technology for stably wirelessly transmitting large amounts of data in an airplane or other type of aircraft.
2. Description of Related Art
In-flight entertainment (“IFE”) systems used in passenger planes in recent years have helped make long-distance flights more enjoyable by providing passengers with in-flight entertainment services such as movies, audio programming, games, and even Internet browsing. The movies, audio programming, Internet data, and other information accessible by these systems are typically stored in an on-board server, and delivered from the server by coaxial cable, optical fiber, or other wired medium as either analog or digital transmissions. IFE equipment generally includes a ceiling-mounted projector and an LCD or other type of video monitor, as well as compact, individual monitors and controllers (handsets) installed at individual passenger seats.
The main transmission cable from the server is generally located in the ceiling, and other ceiling-mounted devices are connected by trunk lines from the main cable. In order to connect to devices located in the floor-mounted seats, large numbers of relay cables are wired through the side walls of the aircraft. Because maximizing the operating rate of high cost airplanes is a major concern for airline companies, airlines frequently change the routes on which aircraft are used and the ticket class configuration of the planes. This necessitates changing the seat positions, which is preferably done in a short time and at low cost. However, because changing the seating configuration means that the relay lines in the side walls must also be changed, changing the seating arrangement takes a long time and is thus expensive. There is, therefore, a need to change from a wired to a wireless transmission medium.
Various technologies for stabilizing wireless transmission have been proposed. In reference patent 1, the antennae of a fixed base station are disposed at positions selected based on the height of each group of RF interference objects that are separated into groups. By appropriately positioning the antennae, the space inside a building or facility can be used effectively and diversity reception, which is effective for broadband transmissions, can be achieved.
In order to afford comprehensive diversity communication with mobile terminals using antenna at two different positions in the fixed base station in a building or facility, reference patent 2 teaches disposing the two antennae so that at least one antenna is substantially parallel to the short side of the wireless service zone being used in order to achieve good diversity reception.
Reference patent 1: Japanese Unexamined Patent Appl. Pub. H03-70220
Reference patent 2: Japanese Unexamined Patent Appl. Pub. H06-13960
Transmitting primarily video information to individual seats inside an aircraft requires significant bandwidth. If a broadcast system that transmits the same content simultaneously to each seat is used and the video signal is sent to each seat at a 5 megabit/second bitrate, the transmission path only requires the same 5 Mb/sec transmission capacity. However, if an on-demand unicast system enabling each user to receive content as desired is used, a transmission path with a capacity exceeding 1 Gb/second must be provided for each of several hundred seats. While the transmission load on the relay lines is not as great as the main trunk line, each relay line supplies anywhere from several to several ten seats and a transmission capacity of from several ten to several 100 megabits/second is therefore required.
Converting this wired system to a wireless system requires building a system that can assure a transmission capacity between several ten to several 100 megabits/second. The technologies taught in reference patents 1 and 2, however, are directed to carrying voice and data traffic within a building or facility and are not suited to the large transmission capacity needed to carry video.
The quality of the content delivered to passengers in an in-flight entertainment system must also be comparable to the playback quality of packaged media, and cannot be jumpy or interrupted. The inside of an airplane is also a difficult environment for enabling stable wireless transmission because the aircraft is populated by several hundred seats and the seating configuration can change frequently. When transmitting only audio and data as described in reference patents 1 and 2 a certain amount of signal degradation is permissible not only for data signals but also audio. As a result, the technologies taught in reference patents 1 and 2 cannot be used to wirelessly transmit high capacity video signals in an in-flight entertainment system with the high quality and stability that are required.